Insulation plays an important role in the energy efficiency and environmental impact of building envelopes. In many cases, polyisocyanurate foam is used for building insulation as it has many advantages, such as relatively low installed cost, good fire resistance and high thermal resistance. As a result, it is important to understand the thermal resistance performance of such foam insulation.
In order to allow for a simple, yet consistent methodology to measure and compare thermal performance, North American manufacturers of building envelope thermal insulation test and report the R-value (a measure of thermal resistance used in the building and construction industry) of their products in compliance with industry standards. Long term thermal resistance (“LTTR”) is an industry measure representing R-value of building insulation comprised of a cellular plastic insulation that contains gases other than air where the composition of the retained gases changes with time. Often, a LTTR of at least 5.4 ft2·hr·° F./BTU·inch (0.936 m2·° C./W@25 mm) is desirable and a minimum design value of 5.7 ft2·hr·° F./BTU·inch (0.988 m2·° C./W@25 mm) has been suggested by the Polyisocyanurate Manufacturers Association (PIMA). A problem with this standard, however, is that it requires measurement of R-value at a mean temperature of 75° F. (23.9° C.). Such a representation of R-value does not reflect performance of foam insulation across the full range of exposure temperatures.
A problem that has been associated with polyisocyanurate foam building insulation is that, unlike some other insulation materials, it has been reported that such insulation exhibits poorer thermal resistance, i.e., reduced R-value, at low temperatures. As a result, it would be desirable to provide methods for designing polyisocyanurate foam-forming compositions that produce a faced rigid foam laminate having a LTTR of at least 5.4 ft2·hr·° F./BTU·inch ((0.936 m2·° C./W@25 mm) at all mean insulation temperatures within the range of from 10° F. to 75° F. (−12.2° C. to 23.9° C.), when measured according to CAN/UL S770-09. The present invention was made in view of the foregoing desire.